1. Field of the Invention
The present invention relates to an electric double layer capacitor, an electrolyte battery, and a method for manufacturing the same.
2. Description of the Related Art
Electric double layer capacitors are devices with excellent charge-discharge behavior.
FIG. 7 is a cross-sectional view showing a cell (2) constituting a conventional electric double layer capacitor (1), as disclosed in JP 2001-351833A, for example. In it, a pair of polarizable electrodes (20) and (21) are stacked, sandwiching a separator (6), with metal collector electrodes (3) and (30) attached to outer sides of the polarizable electrodes (20) and (21). The polarizable electrodes (20) and (21) are composed by adding a conductive polymer, such as polypyrrole, to an active carbon that is in powder or fiber form, hardening this with a bonding material, and pressure forming. The polarizable electrodes (20) and (21) are impregnated with an electrolyte such as sulfuric acid. It is also possible to use a non-aqueous electrolyte as described below instead of an aqueous electrolyte such as sulfuric acid.
A peripheral portion of the polarizable electrodes (20) and (21) is sealed by an insulating sealing member (4) composed of synthetic resin, and this sealing member (4) prevents the electrolyte from leaking out of the cell (2). Ordinarily, the cell (2) comprises two or more horizontally arrayed electric double layer capacitors (1).
When charging, one collector electrode (3) is connected to a positive side of a power source, the other collector electrode (30) is connected to a negative side of a power source, and a dc voltage is applied. Negative ions are attracted to the polarizable electrode (20) connected to the positive-side collector electrode (3), while positive ions are attracted to the polarizable electrode (21) connected to the negative-side collector electrode (3), thereby forming an electric double layer between the polarizable electrodes (3) (30).
When discharging, the collector electrodes (3) and (30) are electrically connected. The electric charge accumulated in the polarizable electrodes (20) and (21) is discharged.
However, in the above-described double layer capacitor, the adhesiveness between the collector electrodes (3) and (30) and the sealing member (4) is low. Therefore, there is a possibility of the electrolyte impregnated in the polarization electrodes (20) and (21) leaking out between the collector electrodes (3) and (30) and the sealing member (4), and of moisture outside the cell (2) entering the inside of the sealing member (4). In particular, it is very common for the sealing member (4) to be formed by abutting a pair of case halves (40) and (41) together and joining them by ultrasonic welding. The electrolyte can easily leak out from between the collector electrodes (3) and (30) and the sealing member (4) during the joining due to pressure vibration caused by the ultrasonic welding.
As shown in FIG. 8, during ultrasonic welding, a horn (5) is applied from above the abutted case halves (40) and (41) and vibrated horizontally. As shown by arrow B, the vibration direction is diagonal with respect to a borderline L between the collector electrodes (3) and (30) and the sealing member (4). By doing this, a peripheral portion of the case halves (40) and (41) is welded in a uniform fashion, applying vibrations in mutually intersecting directions simultaneously within a horizontal plane. When this is done, the electrolyte moves towards the borderline L between the collector electrodes (3) and (30) and the sealing member (4), causing the electrolyte to easily leak, and allowing outside moisture to easily enter the inside of the sealing member (4).
Particularly in the case of non-aqueous electrolytes, entry of moisture from outside causes electrolysis inside the cell (2), leading to a drop in performance as an electric double layer capacitor.
The present invention has as an object to provide an electric double layer capacitor and an electrolyte battery which prevent leaking of the electrolyte and entry of moisture from outside, in particular during ultrasonic welding.